The present invention relates to an electro-photographic photosensitive member, particularly to one characterized by having a protective layer comprising specific particles and a specific resin, and also to a process cartridge and an electro-photographic apparatus including such a photosensitive member.
In recent years, extensive research and development works have been made on electrophotographic photosensitive members using organic photoconductors in view of their advantages, such as high level of safety, excellent productivity and inexpensiveness. Many proposals have been made, and many of them have been commercialized up to now.
Among such photosensitive members using organic photoconductors, those using a photoconductor principally comprising a photoconductive polymer as represented by poly-N-vinylcarbazole and a charge transfer complex formed of 2,4,7-trinitrofluorene, etc., have not been necessarily satisfactory.
On the other hand, a function separation-type electrophotographic photosensitive member wherein separate substances are in charge of a charge-generating function and a charge-transporting function, respectively, has resulted in remarkable improvements in photosensitivity and durability which have been regarded as defects of conventional organic photosensitive members. Further, the function separation-type electrophotographic photosensitive member also has an advantage that the charge-generating substance and the charge-transporting substance respectively allow large latitude of material selection, thus allowing relatively easy production of a photosensitive member having arbitrary desired performances.
As the charge-generating substance, there have been known various azo pigments, polycyclic quinone pigments, phthalocyanine pigments, cyanine colorants, squaline acid dyes, pyrylium salt dyes, etc.
As the charge-transporting substance, pyrazoline compounds, hydrazone compounds, triphenylamine compounds, etc., are known.
On the other hand, accompanying increasing demands for image forming machines capable of providing high-quality images and exhibiting high speed and high durability in recent years, such an organic electrophotographic photosensitive member is also required to exhibit a further increased mechanical durability.
Further, image forming machines, such as printers, copying machines and facsimile apparatus, using electrophotographic photosensitive members are becoming used in a wide variety of fields, and therefore are further required to always provide stable images in various environments, so that the surface layer of the photosensitive member is liable to be exposed to chemical, electrical and mechanical impacts at a higher possibility, thus being required of further performances.
More specifically, an electrophotographic photosensitive member is subjected to a repetition of an image forming cycle including steps of charging, exposure, development, transfer, cleaning, charge removal, etc. An electrostatic latent image formed by the charging and exposure is developed with a fine powdery developer called a toner to form a toner image on the photosensitive member. The toner image is then transferred onto a transfer(-receiving) material, such as paper, but all the toner is not transferred but a portion thereof remains as a residual toner on the photosensitive member.
A large amount of the residual toner, if caused, can promote a further transfer failure to result in a toner image on the transfer material with noticeable lack of portion of image and image uniformity. Further, the residual toner causes problems, such as melt-sticking and filming of the toner onto the photosensitive member. In order to cope with these problems, an electrophotographic photosensitive member is required to have a surface layer with improved releasability.
Further, an electrophotographic photosensitive member is subjected to direct application of electrical and mechanical external forces, so that the photosensitive member is required to be durable against such forces. More specifically, the photosensitive member is required to be durable against the occurrences of surface abrasion and scars due to rubbing and surface layer degradation due to attachment of active substances, such as ozone and NOx, occurring during the charging of the photosensitive member.
In order to comply with the above-mentioned requirements of the photosensitive member, it has been proposed to dispose various protective layers. For example, Japanese Laid-Open Patent Application (JP-A) 57-30846 discloses a protective layer comprising a resin to which a metal oxide is added as electro-conductive powder for resistivity control.
The dispersion of electroconductive powder in such a protective layer of an electrophotographic photosensitive member is performed principally for the purpose of controlling the electrical resistivity of the protective layer per se to prevent an increase in residual potential in the photosensitive member liable to be caused along with the repetition of the electro-photographic image forming cycles. It is known that an appropriate range of volume resistivity of a protective layer is 1010 to 1015 ohm.cm. The resistivity in the above-mentioned range of protective layer is liable to be affected by ionic conduction and is therefore liable to result in a remarkable change in resistivity due to an environmental change. Particularly, in the case of a resinous film containing metal oxide powder dispersed therein, it has been very difficult to keep the resistivity of the protective layer in the above-mentioned range under various environmental conditions since the metal oxide powder surface exhibits a high moisture absorptivity. Further, many resins per se exhibit high moisture absorptivity and are liable to lower the resistivity of the protective layer formed therefrom.
Particularly, in a high-humidity environment, the surface layer of a photosensitive member is liable to have a lower resistivity by standing or repetitive surface-attachment of active substances, such as ozone and NOx, and also cause a lowering in toner releasability, thus causing image defects such as image flow and insufficient image uniformity.
In the case of dispersing electroconductive particles in a protective layer, it is generally preferred that the particles have a particle size (diameter) smaller than the wavelength of light incident thereto, that is, at most 0.3 xcexcm, in order to prevent the scattering of incident light due to the dispersed particles. Moreover, electroconductive particles generally tend to agglomerate with each other when dispersed in a resin solution, are difficult to disperse, and even if once dispersed, are liable to cause secondary agglomeration or precipitation, so that it has been difficult to form a resinous film in which fine particles of at most 0.3 xcexcm in particle size are uniformly dispersed. Further, in order to provide a protective layer with a better transparency and a better uniformity of electro-conductivity, it is particularly preferred to disperse fine particles (of at most 0.1 xcexcm in primary particle size), but such fine particles are liable to exhibit even worse dispersibility and dispersion stability.
In order to alleviate the above-mentioned difficulties, JP-A 1-306857 has disclosed a protective layer containing a fluorine-containing silane coupling agent or titanate coupling agent, or a compound such as C7F15NCO; JP-A 62-295066 has disclosed a protective layer containing metal or metal oxide fine powder subjected to a water-repelling treatment for improved dispersibility and moisture resistance dispersed in a binder resin; and JP-A 2-50167 has disclosed a protective layer containing metal oxide fine powder surface-treated with a titanate coupling agent, a fluorine-containing silane coupling agent or acetoalkoxy-aluminum diisopropylate dispersed in a binder resin.
However, even such a protective layer still shows a lower resistivity to cause image blurring in a high-humidity environment and exhibits insufficient durability against abrasion or scars due to rubbing, thus being not fully satisfactory as a protective layer for providing electrophotographic performances complying with demands for high image qualities in recent years.
On the other hand, the use of fluorinated carbon as moderately electroconductive particles together with various binder resins including a thermosetting phenolic resin for providing a protective layer has been proposed in JP-A 62-19254. However, the resultant protective layer is not sufficient with respect to dispersion of the fluorinated carbon and environmental stability of the resistivity, thus being liable to result in increases in resistivity and residual potential in a low humidity environment, and a lower humidity to cause image blurring in a high humidity environment.
The use of various thermosetting resins, inclusive of a phenolic resin, together with various filler materials, inclusive of a metal oxide, for providing a protective layer, has been proposed in JP-A 5-181299. However, the metal oxide fine particles disclosed therein are non-conductive reinforcing particles preferably having a particle size of 0.05-3 xcexcm. Accordingly, the metal oxide particles are not effective for providing a protective layer exhibiting a low resistivity, and a sufficient consideration has not been paid to the provision of a transparent protective layer.
The inclusion of a charge-transporting substance having a hydroxyl group for providing a controlled resistivity in a protective layer has been proposed in JP-A 10-228126 and JP-A 10-228127.
However, even an electrophotographic photosensitive member provided with such a protective layer has not fully succeeded in exhibiting sufficient durability against various external forces including mechanical forces causing surface abrasion and scars, and sufficient releasability, as required for complying with further demands for higher durability and higher image quality in recent years.
Accordingly, a generic object of the present invention is to provide an electrophotographic photosensitive member having solved the above-mentioned problems of the conventional electrophotographic photosensitive members.
A more specific object of the present invention is to provide an electrophotographic photosensitive member capable of effectively suppressing a lowering in photosensitivity and an increase in residual potential liable to be caused by provision of a protective layer.
Another object of the present invention is to provide an electrophotographic photosensitive member which has a surface layer exhibiting excellent releasability and excellent durability against abrasion and scars and thus can maintain high-quality images.
A further object of the present invention is to provide a process cartridge and an electro-photographic apparatus including such an electro-photographic photosensitive member.
According to the present invention, there is provided an electrophotographic photosensitive member, comprising: a support, a photosensitive layer and a protective layer in this order; wherein said protective layer comprises a cured phenolic resin and a charge-transporting compound having at least one group selected from the group consisting of hydroxyalkyl groups, hydroxyalkoxy groups and hydroxyphenyl groups capable of having a substituent.
According to the present invention, there is further provided a process cartridge, comprising: the above-mentioned electrophotographic photosensitive member and at least one means selected from the group consisting of charging means, developing means and cleaning means; said electrophotographic photo-sensitive member and said at least one means being integrally supported and detachably mountable to a main assembly of an electrophotographic apparatus.
The present invention further provides an electrophotographic apparatus, comprising: the above mentioned electrophotographic photosensitive member, and charging means, developing means and transfer means respectively disposed opposite to the electro-photographic photosensitive member.